Margaritifera margaritifera - (Linnaeus, 1758)
Eastern Pearlshell
Other English Common Names: Eastern Pearl Mussel, Freshwater Pearl Mussel
Taxonomic Status: Accepted
Related ITIS Name(s): Margaritifera margaritifera (Linnaeus, 1758) (TSN 80371)
French Common Names: mulette perlière de l?Est
Unique Identifier: ELEMENT_GLOBAL.2.115572
Element Code: IMBIV27030
Informal Taxonomy: Animals, Invertebrates - Mollusks - Freshwater Mussels
 
Kingdom Phylum Class Order Family Genus
Animalia Mollusca Bivalvia Unionoida Margaritiferidae Margaritifera
Genus Size: B - Very small genus (2-5 species)
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Concept Reference
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Concept Reference: Turgeon, D.D., J.F. Quinn, Jr., A.E. Bogan, E.V. Coan, F.G. Hochberg, W.G. Lyons, P.M. Mikkelsen, R.J. Neves, C.F.E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F.G. Thompson, M. Vecchione, and J.D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society Special Publication 26, Bethesda, Maryland: 526 pp.
Concept Reference Code: B98TUR01EHUS
Name Used in Concept Reference: Margaritifera margaritifera
Taxonomic Comments: The family Margaritiferidae is recognized based on the recent work of Smith (1986) and Smith and Wall (1984). The monotypic genus Cumberlandia has generally has been classified in the family Margaritiferidae; however, preliminary analyses of electrophoretic data led Davis and Fuller (1981) to lump the margaritiferids with the Unionidae. Smith and Wall (1984) reinstated the Margaritiferidae to familial rank following and extensive examination and analysis of morphological characters. Some anatomical data on stomach anatomy (Smith, 1986) indicates Cumberlandia may require reduction to subgeneric level. This is supported by Davis and Fuller (1981), Ziuganov et al. (1994), Smith (2001), and Huff et al. (2004). Smith (2001) analyzied the taxonomic placement of the margaritiferid genera, recognizing Pseudunio, Margaritifera, and Margaritinopsis as valid based largely on morpological characters; with Margaritifera margaritifera the only species in the genus Margaritifera. Contrary to Smith (2001), Huff et al. (2004) investigated phylogenetic relationships using sequence data from five molecular markers and concluded recognition of of at least Margaritifera margaritifera, Margaritifera laevis, Margaritifera falcata, and Margaritifera auricularia with the following relationships: Cumberlandia + Margaritifera auricularia; Margaritifera falcata (Margaritifera marrianae + Margaritifera laevis); and to a lesser degree Dahurinaia dahurica + Margaritifera margaritifera. More recently, to monophyletic clades have been identified within Margaritiferidae based on COI data: one including M. margaritifera, M. dahurica, M. falcata, and M. laevis; and a second comprising M. auricularia and M. marocana (Araujo et al., 2009).
Conservation Status
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NatureServe Status

Global Status: G4
Global Status Last Reviewed: 31Dec2011
Global Status Last Changed: 04Dec1998
Rounded Global Status: G4 - Apparently Secure
Reasons: This species has a very large distribution with some very large healthy populations remaining in North America and some parts of Europe; has suffered significant widespread declines in occupancy, range extent, and number of occurrence across its entire range in Europe, however, including several national extirpations, with less serious declines in the U.S. and Canada.
Nation: United States
National Status: N4 (16Jul1998)
Nation: Canada
National Status: N4N5 (01Aug2017)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Connecticut (SU), Idaho (SNR), Maine (SNR), Massachusetts (S4), New Hampshire (S3?), New Jersey (SX), New York (S2), Pennsylvania (S1), Rhode Island (S2), Vermont (S2), Wyoming (SNR)
Canada Labrador (SU), New Brunswick (S4), Newfoundland Island (S4), Nova Scotia (S2), Prince Edward Island (S1S2), Quebec (S3)

Other Statuses

Committee on the Status of Endangered Wildlife in Canada (COSEWIC): Candidate (Low) (10Jul2017)
IUCN Red List Category: EN - Endangered
American Fisheries Society Status: Special Concern (01Jan1993)

NatureServe Global Conservation Status Factors

Range Extent: >2,500,000 square km (greater than 1,000,000 square miles)
Range Extent Comments: This species has a circumboreal distribution in northern Europe, eastern North America, and Eurasia. Its range includes the arctic and temperate regions of western Russia, westwards through Europe to the north-eastern seaboard of North America and southwards to the Iberian peninsula and "central" Europe. In North America it is distributed from Newfoundland and Labrador down to Pennsylvania (Burch, 1975) and Delaware and west to the Appalachian mountains (Ziuganov et al., 1994). The eastern pearlshell is widespread in New England and the Canadian Maritime Provinces (Nedeau et al., 2000; Clarke, 1981; Smith, 2000; Fichtel and Smith, 1995; Raithel and Hartenstein, 2006). The current status across its range is as follows: USA- declining and of special concern but somewhat stable in New England, Canada- some large populations remain and threats are few, Portugal- presumed extinct, Spain- serious decline with one or two functional populations including recently in the Iberian Peninsula (Velasco et al., 2006), France- still present but scarce in most of its former range, Belgium- extirpated, Germany- still present but serious decline although some functional populations in Bavaria, Austria- serious decline with 1-2 functional populations, Czech Republic- serious decline with one functional population, Norway- serious decline especially in the south, Denmark- extirpated, Sweden- serious decline with appreciable recruitment at only two sites, Finland- 75% populations lost with ca 8 functional populations, Russia- serious decline with four populations of over 1 million remaining, Eire- serious decline with little recruitment, England- only one common population remaining with limited recruitment, Wales- only one population above 3000 individuals and very few juveniles, Northern Ireland- 90% population lost and almost no recruitment, Scotland- serious decline with ca 10 fully functional populations (Young et al., 2001).

Area of Occupancy: >12,500 4-km2 grid cells
Area of Occupancy Comments:  

Number of Occurrences: > 300
Number of Occurrences Comments: In Rhode Island, this species occurs primarily in headwater streams of the Pawcatuck River basin and a few sites in the Blackstone River and Pawtuxet River basins although these latter two basin populations may now be extirpated (Raithel and Hartenstein, 2006). In Maine, it is known from nearly every watershed in every county except the Sagadahoc (Nedeau et al., 2000). In Massachusetts, it is relatively common in small to medium sized streams of the Connecticut River drainage but uncommon elsewhere. It also persists in the Merrimack drainage, but is now rare; and in southeastern portions of Massachusetts (Smith, 2000). Three newly discovered individuals were discovered in the Delaware River, Pennsylvania (Lellis et al., 2007). In Vermont, it is found in the Winooski River and Lewis Creek systems of the Lake Champlain drainage, and the West River, Passumpsic River, and Nulhegan River systems of the Connecticut River drainage (Fichtel and Smith, 1995). In Connecticut, it is found in many major watersheds (recently absent from Housatonic, south coast drainages, and Thames River drainage- J. Cordeiro, pers. obs., 2006) but is most common in the northern and northwestern parts of the state (Nedeau and Victoria, 2003). In New York, it is widespread along the margins of the Adirondacks, where it has been seen in Oneida Lake, Fish Creek, Black River, Grass River, and Lake Champlain basins; and undiscovered populations may occur throughout eastern New York in some trout streams (Strayer and Jirka, 1997). Erickson (2001) recorded the species at more than 50 sites in north-flowing Adirondack drainage tributary to the St. Lawrence River in New York. In Pennsylvania it only reamains in a few sites in the Delaware River drainage (Spoo, 2008). In Canada, this species is considered secure throughout most of its eastern Canadian range including most of New Brunswick (Hanson and Locke, 2000; Sabine et al., 2004), central, northern, and eastern Nova Scotia (Clark and Rick, 1964), throughout Newfoundland Island, and Prince Edward Island (Davis, 1999) and less common and sensitive to acid rain in Quebec; in Labrador it supposedly occurs throughout the area south from Lake Melville to the Straits of Belle Isle (Metcalfe-Smith and Cudmore-Vokey, 2004). Martel et al. (2004) recorded this species in Lac Philippe, Gatineau Park, southwestern Quebec. Although reported for Saskatchewan in the Carrot River as a highly polished single valve, no other specimens have been found and this specimen likely originated from elsewhere (Metcalfe-Smith and Cudmore-Vokey, 2004). In western Europe, populations are in the Kola peninsula of Russia (Ziuganov et al., 2001), Scandinavia and the British Isles (Young and Williams, 1983), northern (Bauer, 1986) and northwest Spain (Outeiro et al., 2008), and Portugal (Reis, 2003). In central Europe, populations are in the Elbe, danube, Weser, Main/Rhine, and Maas (in Germany, Czech Republic, Austria, Belgium, Luxenbourg) with small populations in France (Massiv Central, Arquitaine, Brittany) and Baltic states; and "functional" populations in Germany (Lutter), Czech Republic (Blanice), Portugal (Douro tribs.), Scotland (several), Ireland (western), northern Scandinavia (Pikku-Luiro), and Russia (Varzuga) (see Geist, 2010).

Population Size: >1,000,000 individuals
Population Size Comments: Remaining populations in most of Europe are characterised by an ageing cohort of individuals with little or no recent recruitment (Beasley and Roberts, 1996; 1999; Beasley et al., 1998). The largest population known, on the Varzuga River in Northern Russia, is estimated at approximately 51 million over a 200 km stretch of river (Ziuganov et. al. 1998). Some northeastern Canadian populations have numbers in the thousands (Metcalfe-Smith and Cudmore-Vokey, 2004).

Number of Occurrences with Good Viability/Integrity: Very many (>125)
Viability/Integrity Comments: In Europe, Scotland maintains some of the best remaining populations compared to widespread decline across the continent in other countries (Cosgrove et al., 2000), but the largest populaton (with several million individuals) and an intact age structure occurs in Russian rivers of the Kola peninsula (Ziuganov et al., 2001). Large populations are also reported from Scandinavia and the British Isles (Young and Williams, 1983). Self-sustaining populations of mussels of international importance outside Britain and Ireland are now found chiefly in Canada, north-west Russia and north-east Scandanavia (Araujo and Ramos, 2001; Young et al., 2000).

Overall Threat Impact: High
Overall Threat Impact Comments: Potential threats include overcollecting for the pearl industry and alteration of habitat. Declines in Europe are attributed to increasing pollution and habitat alteration, drainage of wetlands, building of dams, and canalization of rivers. Although predation may be a minor threat to populations in North America, there is no direct evidence to suggest that natural predation causes any significant mortality in rivers in Scotland (despite minor, opportunistic predation by otter, mink, oystercatcher and hooded crow) (Cosgrove et al., 2007). Hastie et al. (2003) outline how climate change might potentially negatively affect populations in northern Europe such as through flooding, temperature change, habitat loss, sea level rise, host fish stock changes, etc. Failure to recruit - a figure of at least 20% of the population between 10 - 20 years old in much of Europe is often used as an estimate of what constitutes a viable mussel population (Young et al., 2000; Young et al., 2001). In addition, there is recent evidence to suggest that illegal and destructive pearl fishing has been occurring at practically every British and Irish river (Young et al., 2000). There are numerous examples of the detrimental effects of pollution on M. margaritifera (Ziuganov et al., 1994). One of the factors implicated in the decline of M. margaritifera in the UK has been the destruction of suitable river habitat through modification of river beds for drainage and flow regulation schemes and fisheries management (Cosgrove et al., 2000; Young et al., 2000). Long-term survival clearly depends on availability of host species (Hastie and Cosgrove, 2001). Pearl mussel populations may be vulnerable to climate change through increases in temperatures (it is a cold water species) and through changes in rainfall resulting in a sequence of higher water levels and flooding followed by low water levels and channel bed exposure; although this is speculative.

Short-term Trend: Decline of 30-70%
Short-term Trend Comments: Historically, the species was extremely common in suitable rivers throughout most of its range in Europe but its range and abundance is now much reduced. Analysis of British records show that there has been a dramatic and sustained decline in the species, which was especially marked in England and Wales (Cosgrove et al., 2000). A recent survey found that M. margaritifera were extinct in approximately two thirds of the Scottish rivers in which they were original found (Cosgrove et al., 2000). Information on the current distribution of M. margaritifera in Ireland suggests that the species has undergone a large decline in both absolute numbers and range (Cosgrove et al., 2000). Of particular concern is the virtual extinction of the hard-water form Margaritifera margaritifera durrovensis (Costello et al., 1998). The species has suffered significant declines in the late 1900's in North and Central Europe (Wells et. al., 1983), but is doing well in other parts of range. Raithel and Hartenstein (2006) documented declines in Rhode Island populations including some Pawcatuck River basin populations and complete extirpation from the Pawtuxet and Blackstone River basins in the 1990s. In Maine, although the species is widely distributed, it is not often abundant, frequently with only a few old individuals and little evidence of recruitment (Nedeau et al., 2000).

Long-term Trend: Decline of 50-70%
Long-term Trend Comments: The species has suffered significant declines in the late 1900's in North and Central Europe (Wells et. al., 1983), but is doing better in other parts of range. Bauer (1986; 1988) estimates a 95-100% decline in known populations in central and southern Europe by the 1990s. Declines have also occurred in North America but not nearly to the vast extent that they have in Europe (Young et al., 2001; Araujo and Ramos, 2001). The current status across its range is as follows: USA- declining and of special concern but somewhat stable in New England, Canada- some large populations remain and threats are few, Portugal- presumed extinct, Spain- serious decline with one or two functional populations, France- still present but scarce in most of its former range, Belgium- extirpated, Germany- still present but serious decline although some functional populations in Bavaria, Austria- serious decline with 1-2 functional populations, Czech Republic- serious decline with one functional population, Norway- serious decline especially in the south, Denmark- extirpated, Sweden- serious decline with appreciable recruitment at only two sites, Finland- 75% populations lost with ca 8 functional populations, Russia- serious decline with four populations of over 1 million remaining, Eire- serious decline with little recruitment, England- only one common population remaining with limited recruitment, Wales- only one population above 3000 individuals and very few juveniles, Northern Ireland- 90% population lost and almost no recruitment, Scotland- serious decline with ca 10 fully functional populations (Young et al., 2001). Ortmann (1919) cites Pennsylvania occurrences in the Schuykill basin and now it occurs there in a single site. It once likely occurred in the Hackensack River in Rockland County, New York, into neighboring New Jersey but it is likely gone due to intensive residential development (summarized in Strayer and Jirka, 1997).

Intrinsic Vulnerability: Moderately vulnerable
Intrinsic Vulnerability Comments: Because this species is extremely long-lived (over 100 years) and reaches sexual maturity at about 20 years (Bauer, 1987), populations can effectively be functionally extinct if they are either not reproducing or host fish are not present; although this might not be evident unless extremely long-term monitoring was in place. In many cases, the greatest concern is lack of juvenile reproduction in European populations over the past 30-50 years leading to fragmentation and isolation of otherwise healthy populations.

Environmental Specificity: Narrow. Specialist or community with key requirements common.
Environmental Specificity Comments: Typically, this species is intolerant of eutrophication and prefers flowing water in softwater streams with low calcium levels (Bauer, 1988; Buddensiek, 1995).

Other NatureServe Conservation Status Information

Distribution
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Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) This species has a circumboreal distribution in northern Europe, eastern North America, and Eurasia. Its range includes the arctic and temperate regions of western Russia, westwards through Europe to the north-eastern seaboard of North America and southwards to the Iberian peninsula and "central" Europe. In North America it is distributed from Newfoundland and Labrador down to Pennsylvania (Burch, 1975) and Delaware and west to the Appalachian mountains (Ziuganov et al., 1994). The eastern pearlshell is widespread in New England and the Canadian Maritime Provinces (Nedeau et al., 2000; Clarke, 1981; Smith, 2000; Fichtel and Smith, 1995; Raithel and Hartenstein, 2006). The current status across its range is as follows: USA- declining and of special concern but somewhat stable in New England, Canada- some large populations remain and threats are few, Portugal- presumed extinct, Spain- serious decline with one or two functional populations including recently in the Iberian Peninsula (Velasco et al., 2006), France- still present but scarce in most of its former range, Belgium- extirpated, Germany- still present but serious decline although some functional populations in Bavaria, Austria- serious decline with 1-2 functional populations, Czech Republic- serious decline with one functional population, Norway- serious decline especially in the south, Denmark- extirpated, Sweden- serious decline with appreciable recruitment at only two sites, Finland- 75% populations lost with ca 8 functional populations, Russia- serious decline with four populations of over 1 million remaining, Eire- serious decline with little recruitment, England- only one common population remaining with limited recruitment, Wales- only one population above 3000 individuals and very few juveniles, Northern Ireland- 90% population lost and almost no recruitment, Scotland- serious decline with ca 10 fully functional populations (Young et al., 2001).

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
Endemism: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States CT, ID, MA, ME, NH, NJextirpated, NY, PA, RI, VT, WY
Canada LB, NB, NF, NS, PE, QC

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
CT Fairfield (09001), Hartford (09003), Litchfield (09005), Middlesex (09007), New London (09011), Tolland (09013), Windham (09015)
NY Clinton (36019), Delaware (36025), Essex (36031), Lewis (36049), Madison (36053), Oswego (36075), Rockland (36087), Saratoga (36091), St. Lawrence (36089)
PA Berks (42011), Monroe (42089)*, Schuylkill (42107)
RI Washington (44009)*
VT Addison (50001), Caledonia (50005), Chittenden (50007), Essex (50009), Washington (50023), Windham (50025)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
01 Upper Connecticut (01080101)+, Passumpsic (01080102)+, West (01080107)+, Lower Connecticut (01080205)+, Farmington (01080207)+, Pawcatuck-Wood (01090005)+, Quinebaug (01100001)+, Shetucket (01100002)+, Thames (01100003)+*, Saugatuck (01100006)+
02 Hudson-Hoosic (02020003)+, Hackensack-Passaic (02030103)+, Upper Delaware (02040101)+, Middle Delaware-Mongaup-Brodhead (02040104)+*, Schuylkill (02040203)+, Chenango (02050102)+
04 Oneida (04140202)+, Grass (04150304)+, Winooski River (04150403)+, Ausable River (04150404)+, Lake Champlain (04150408)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
U.S. Distribution by Watershed (based on multiple information sources) Help
Ecology & Life History
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Basic Description: a freshwater mussel
Reproduction Comments: This species has a very high fecundity (upward of 17 million glochidia produced annually) (Bauer, 1987) and the smallest glochidia. Mean age of sexual maturity is 20 years and individuals are known to live over 100 years (Bauer, 1987) and even the oldest individuals show no reduction in fecundity in regard to production of glochidia (Young and Williams, 1983; Hastie and Young, 2003). The host fish in central Europe are the huchen (Hucho hucho), brown trout (Salmo trutta), Eurasian dace (Phoxinus phoxinus phoxinus), and Atlantic salmon (Salmo salar) (Bauer, 1987; Harms, 1907). Additional hosts in the United States include the cutthroat trout (Oncorhynchus clarki), coho salmon (Oncorynchus kisutch), rainbow trout (Oncorhynchus mykiss), sockeye salmon (Oncorhynchus nerka), chinook salmon (Oncorhynchus tshawytscha), brook trout (Salvelinus fontinalis) (Bauer, 1987; Karna and Millemann, 1978; Meyers and Millemann, 1977; Wells et. al., 1983; Young et al., 1987; Young and Williams, 1984). Young and Williams (1984), however claim rainbow trout is unsuitable. Only sea trout, brown trout, and Atlantic salmon are known to host complete metamorphosis in Europe with brown trout the main host species in Ireland and Germany and brook charr acting as host in north America (Skinner et al., 2003). Also brook trout is an unsuitable host in Europe despite being an important host in North America (Ziuganov et al., 1994).
Ecology Comments: It is thought to be the longest-lived invertebrate animal. Its average life span in Europe is 93 years old and a specimen in Russia was determined to be at least 114 years old (Ziuganov et. al. 1998).
Habitat Type: Freshwater
Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: N
Riverine Habitat(s): BIG RIVER, CREEK, MEDIUM RIVER, Moderate gradient
Special Habitat Factors: Benthic
Habitat Comments: Generally live buried in clean, mixed stable substrate in fast-flowing unpolluted streams and rivers , but an unusual reproductively viable population in Shetland, Scotland, found recently (Cosgrove and Harvey, 2003) in a fen habitat in peat substrate is atypical.
Phenology Comments: Life span ranges from 30-167 years and maximum size from 30-162 mm (Hastie et al., 2000). Ages of M. margaritifera determined from growth lines sometimes exceed 100 years in Europe (Bauer, 1992; Hendelberg, 1960).Populations in the southern parts of the range typically reach a smaller maximum size in a shorter period and reproduce at a younger age than northern populations (Bauer, 1992).
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: Conservation management strategies have been outlined by Geist (2010) at the individual/population (assessment of inbreeding coefficiends and population uniqueness, gene flow, avoidance of genetic effects in captive breeding, mapping of distribution, assessment of life hsitory and edmography, assessment of local impacts, identification of stakehoulders, assessment of effects of local management), species (development of genetic markers, non-destructive sampling techniques, definition of Conservation Units, recommendation of conservation strategies supporting breeding and culturing techniques, assessment of life-stage specific importance of decline factors, standardizatino of field sampling protocols, ecological conservation prioritization, food requirements of juveniles), and global (testing links between genetic diversity with co-occurring species, mergint genetic and ecological data, dexidions on biodvierstiy hotspots, testing effects of introduction/extinction on ecosystem function, decisions on protected areas) levels.
Population/Occurrence Delineation
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Group Name: Freshwater Mussels

Use Class: Not applicable
Minimum Criteria for an Occurrence: Occurrences are based on some evidence of historical or current presence of single or multiple specimens, including live specimens or recently dead shells (i.e., soft tissue still attached and/or nacre still glossy and iridescent without signs of external weathering or staining), at a given location with potentially recurring existence. Weathered shells constitute a historic occurrence. Evidence is derived from reliable published observation or collection data; unpublished, though documented (i.e. government or agency reports, web sites, etc.) observation or collection data; or museum specimen information.
Mapping Guidance: Based on the separation distances outlined herein, for freshwater mussels in STANDING WATER (or backwater areas of flowing water such as oxbows and sloughs), all standing water bodies with either (1) greater than 2 km linear distance of unsuitable habitat between (i.e. lotic connections), or (2) more than 10 km of apparently unoccupied though suitable habitat (including lentic shoreline, linear distance across water bodies, and lentic water bodies with proper lotic connections), are considered separate element occurrences. Only the largest standing water bodies (with 20 km linear shoreline or greater) may have greater than one element occurrence within each. Multiple collection or observation locations in one lake, for example, would only constitute multiple occurrences in the largest lakes, and only then if there was some likelihood that unsurveyed areas between collections did not contain the element.

For freshwater mussels in FLOWING WATER conditions, occurrences are separated by a distance of more than 2 stream km of unsuitable habitat, or a distance of more than 10 stream km of apparently unoccupied though suitable habitat. Standing water between occurrences is considered suitable habitat when calculating separation distance for flowing water mussel species unless dispersal barriers (see Separation Barriers) are in place.

Several mussel species in North America occur in both standing and flowing water (see Specs Notes). Calculation of separation distance and determination of separation barriers for these taxa should take into account the environment in which the element was collected. Juvenile mussels do not follow this pattern and juveniles are typically missed by most standard sampling methods (Hastie and Cosgrove, 2002; Neves and Widlak, 1987), therefore juvenile movement is not considered when calculating separation distance.

Separation Barriers: Separation barriers within standing water bodies are based solely on separation distance (see Separation Distance-suitable, below). Separation barriers between standing water bodies and within flowing water systems include lack of lotic connections, natural barriers such as upland habitat, absence of appropriate species specific fish hosts, water depth greater than 10 meters (Cvancara, 1972; Moyle and Bacon, 1969) or anthropogenic barriers to water flow such as dams or other impoundments and high waterfalls.
Separation Distance for Unsuitable Habitat: 2 km
Separation Distance for Suitable Habitat: 10 km
Alternate Separation Procedure: None
Separation Justification: Adult freshwater mussels are largely sedentary spending their entire lives very near to the place where they first successfully settled (Coker et al., 1921; Watters, 1992). Strayer (1999) demonstrated in field trials that mussels in streams occur chiefly in flow refuges, or relatively stable areas that displayed little movement of particles during flood events. Flow refuges conceivably allow relatively immobile mussels to remain in the same general location throughout their entire lives. Movement occurs with the impetus of some stimulus (nearby water disturbance, physical removal from the water such as during collection, exposure conditions during low water, seasonal temperature change or associated diurnal cycles) and during spawning. Movement is confined to either vertical movement burrowing deeper into sediments though rarely completely beneath the surface, or horizontal movement in a distinct path often away from the area of stimulus. Vertical movement is generally seasonal with rapid descent into the sediment in autumn and gradual reappearance at the surface during spring (Amyot and Downing, 1991; 1997). Horizontal movement is generally on the order of a few meters at most and is associated with day length and during times of spawning (Amyot and Downing, 1997). Such locomotion plays little, if any, part in the distribution of freshwater mussels as these limited movements are not dispersal mechanisms. Dispersal patterns are largely speculative but have been attributed to stream size and surface geology (Strayer, 1983; Strayer and Ralley, 1993; van der Schalie, 1938), utilization of flow refuges during flood stages (Strayer, 1999), and patterns of host fish distribution during spawning periods (Haag and Warren, 1998; Watters, 1992). Lee and DeAngelis (1997) modeled the dispersal of freshwater into unoccupied habitats as a traveling wave front with a velocity ranging from 0.87 to 2.47 km/year (depending on mussel life span) with increase in glochidial attachment rate to fish having no effect on wave velocity.

Nearly all mussels require a host or hosts during the parasitic larval portion of their life cycle. Hosts are usually fish, but a few exceptional species utilize amphibians as hosts (Van Snik Gray et al., 2002; Howard, 1915) or may metamorphose without a host (Allen, 1924; Barfield et al., 1998; Lefevre and Curtis, 1911; 1912). Haag and Warren (1998) found that densities of host generalist mussels (using a variety of hosts from many different families) and displaying host specialists (using a small number of hosts usually in the same family but mussel females have behavioral modifications to attract hosts to the gravid female) were independent of the densities of their hosts. Densities of non-displaying host specialist mussels (using a small number of hosts usually in the same family but without host-attracting behavior) were correlated positively with densities of their hosts. Upstream dispersal of host fish for non-displaying host specialist mussels could, theoretically, transport mussel larvae (glochidia) over long distances through unsuitable habitat, but it is unlikely that this occurs very often. D. Strayer (personal communication) suggested a distance of at least 10 km, but a greater distance between occurrences may be necessary to constitute genetic separation of populations. As such, separation distance is based on a set, though arbitrary, distance between two known points of occurrence.

Date: 18Oct2004
Author: Cordeiro, J.
Notes: Contact Jay Cordeiro (jay_cordeiro@natureserve.org) for a complete list of freshwater mussel taxa sorted by flow regime.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 31Dec2011
NatureServe Conservation Status Factors Author: Cordeiro, J. (2011); Morrison, M. (1998)
Management Information Edition Date: 20Apr2010
Management Information Edition Author: Cordeiro, J.
Element Ecology & Life History Edition Date: 31Dec2011
Element Ecology & Life History Author(s): Cordeiro, J.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
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  • Araujo, R. and M.A. Ramos. 2001. Action Plan for Margaritifera margaritifera. Council of Europe. T-PVS (2000) 10. Strasbourg, 38 pp.

  • Araujo, R., C. Toledo, D. Van Damme, M. Ghamizi, and A. Machordom. 2009. Margaritifera marocana (Pallary, 1918): A valid species inhabiting Moroccan rivers. Journal of Molluscan Studies 75:95-101.

  • Bauer, G. 1986. The status of the freshwater pearl mussel Margaritifera margaritifera L. in the south of its European range. Biological Conservation, 38: 1-9.

  • Bauer, G. 1987. Reproductive strategy of the freshwater pearl mussel Margaritifera margaritifera. Journal of Animal Ecology 56:691-704.

  • Bauer, G. 1987a. Reproductive strategy of the freshwater pearl mussel Margaritifera margaritifera. Journal of Animal Ecology 56: 691-704.

  • Bauer, G. 1987b. The parasitic stage of the freshwater pearl mussel (Margaritifera margaritifera L.). II. Susceptibility of brown trout. Archiv für Hydrobioligie, Supplement 76: 403-412.

  • Bauer, G. 1988. Threats to the freshwater pearl mussel Margaritifera margaritifera L. in central Europe. Biological Conservation, 45: 239-253.

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